Circular acceleration apparatus, electromagnetic wave generator and electromagnetic-wave imaging system

ABSTRACT

An objective is to provide a circular acceleration apparatus that can accelerate higher currents as well as avoid complex controlling of a deflecting magnetic field generated by an electron deflection unit. The circular acceleration apparatus is provided, which comprising a circular accelerator  2  including an electron acceleration unit  13  and a deflection-magnetic-field generating unit  14 ; an electron generator  1 , to which a pulsed voltage is applied, to generate electrons for injecting to the circular accelerator  2 ; and a circuit element which generates the pulsed voltage for providing to the electron generator  1  by making the pulsed voltage applied to the electron generator  1  have at least one of a slow rising edge and a slow falling edge.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a circular acceleration apparatus thatcan accelerate large-current electron beams, an electromagnetic wavegenerator that generate electromagnetic waves such as X-rays by makingelectrons accelerated by the circular acceleration apparatus collidewith a target, and an electromagnetic-wave imaging system that produceradioscopic images of human bodies, semiconductors and the like, usingX-rays and such generated by the electromagnetic wave generators.

2. Description of the Related Art

In the description below, it is assumed that a circular accelerationapparatus is configured with a circular accelerator, an electroninjection unit and a power supply necessary for operating them. Thecircular accelerator handles electrons generated by an electrongenerator as injection electrons, and accelerates the injectionelectrons until they have a predetermined energy, while making them movein their orbits; it may not necessarily be circular. For convenience,the term “circular” is given because electrons circulate in orbits.

In electromagnetic wave generators that use the circular accelerators togenerate X-rays and such, betatron accelerators and synchrotronaccelerators such as electron storage rings have been used as thecircular accelerators. However, when the betatron accelerators are used,increase of current is difficult due to effects of Coulomb repulsionbetween electrons, resulting in a low electromagnetic wave strength ofX-rays and such generated by making electrons collide with a target, sothat it has been difficult to apply to industry and medical fields theelectromagnetic wave generators using the accelerators. When thesynchrotron accelerators are used as radiation sources, theelectromagnetic waves generated thereby are intense, but have lowenergy; it has been difficult to apply those to the industry and medicalfields. Also, when synchrotron accelerators are used in order togenerate highly-energized electromagnetic waves, a method of not usingsynchrotron radiation, but making electrons collide with a target is tobe adopted; however, the method brings the same difficulties as thosewhen the betatron accelerators are used, in that it is difficult toincrease current, so that the strength of the generated electromagneticwaves such as X-rays becomes low; therefore, it has been difficult toapply to the industry and medical fields the electromagnetic wavegenerators using the synchrotron accelerators as highly energized ones.

In order to improve the situation described above, an electromagneticwave generator using a so-called hybrid accelerator has been proposed inJapanese Patent Laid-Open No. 2004-296164 (Patent Document 1). Thehybrid accelerator is the one that employs such an acceleration methodas follows: while an acceleration means is accelerating electrons froman instant when their injection into the accelerator begins, adeflecting magnetic field generated by deflection electromagnetsincluded in the accelerator is kept constant during an injection period,and is controlled to change after finishing the injection. In thisaccelerator, stable electron orbits exist spreading out over a broadradial range; therefore, when electrons are injected in the waydescribed above, the electrons move stably in orbits each having adifferent diameter depending on their injected instances during theinjection period. Therefore, the accelerator makes the electrons move inorbits spreading over a wide orbital range. Thereby, the spatial densityof electrons can be lowered, resulting in less Coulomb repulsion amongthe electrons, which will enable large-current acceleration.

The hybrid accelerator adopts as an accelerating means, so-calledinduction acceleration by an electric field that an acceleratingmagnetic field induces. FIG. 10 shows variations with time ofdeflection-magnetic-field strength and acceleration-magnetic-fieldstrength according to the invention of Patent document 1. In FIG. 10,‘41’ is the acceleration-magnetic-field strength variation with respectto time, ‘42’, that of the deflection-magnetic-field strength; it isassumed that injecting operations are performed in a pulsational manner.Here, “injecting operations are performed in a pulsational manner” meansthat each injection is performed during a predetermined period after apulse of a rectangular waveform reaches its peak wave-height value. Morespecifically, because the pulse rises to its peak value immediatelyafter it has been generated, the injection period is set as follows:injection starts after a specific time—from an instant at which thepulse has been applied to an instant at which the pulse reaches itspeak—has passed, and continues until a specific time has elapsed whilethe pulse peak value is held. Because the acceleration-magnetic-fieldstrength 41 begins to increase from an instant when the injection ofelectrons starts, the electrons have been accelerated from the instantwhen they have been injected. Meanwhile, the deflection-magnetic-fieldstrength 42 is controlled to stay at a constant value from the instantof the injection start to an instant of the injection end; as soon asthe injection ends, the strength 42 is controlled to begin to increase,similarly to the acceleration-magnetic-field strength 41. While thedeflection-magnetic-field strength 42 stays at the constant value, theinjected electrons that have the same energy as each other areaccelerated immediately after their injection, and their deflectioncurvatures gradually become larger. Therefore, at the instant ofinjection end, each of the electrons has been accelerated differentlydepending on its injected instant during the injection period; theinjection electrons move in orbits spreading out radially. Because theelectrons continue to be thereafter accelerated so as to have apredetermined energy, the radially spread orbits are further expandedradially. After the end of the injection, the deflection-magnetic-fieldstrength 42 increases; the degree of the orbit radial expansion usuallybecomes less than that during the injection. Once the electrons havebeen accelerated to have the predetermined energy, the radii of theelectron orbits can be expanded by, for example, controlling thedeflection-magnetic-field strength 42 at a constant value and the like.

When a target is placed in the way of an orbit having a predeterminedradius out of the ones in which the electrons can move around stably,the radii of the electron orbits being changed, the electron beams cancollide with the target in a controlled manner, so that electromagneticwaves such as X-rays are generated by the collision. Here, because thetarget has a certain area, the electrons moving in orbits within aspecific radial range are ready to be capable of colliding with thetarget. Such orbits will be referred as collision orbits, hereinafter.

Even while the radii of the electron orbits are being changed, electronsare diverged radially and are moving in orbits; by gradually changingthe radii of the orbits, the electron beams can continue to collide withthe target, so that X-rays can be generated continuously. Here, all theelectrons that have collided with the target do not always disappear,but electrons that have reduced energy remain there after theircollision. Because in general, the residual electrons also have energiesin the range of enabling stable movement in orbits, some of theelectrons can be recharged with sufficient energy from the accelerationmagnetic field every turn, so as to return to a collision orbit.Therefore, using the accelerator, electromagnetic waves can be generatedefficiently utilizing electrons moving in orbits (refer to Patentdocument 1).

As has been described, in the accelerators, because the electrons havestable radially-spread-out orbits, causing less Coulomb repulsionbetween electrons, it becomes easy to accelerate large currents; becausethe position of the orbits can be changed, while maintaining conditionsfor electrons to move stably in orbits by controlling theacceleration-magnetic-field strength and the deflection-magnetic-fieldstrength, it becomes possible for electrons moving in orbits to collideefficiently with the target. Thereby, it becomes possible to increasethe strength of the electromagnetic wave such as X-rays generated by theaccelerator. So far, a hybrid accelerator has been described as atypical example, it is not limited to the hybrid accelerator thatcurrent can be increased by increasing the radii of electron orbits. Anytype of circular accelerator has more or less a certain radial range oforbits in which electrons move stably; therefore, it is also possible ina similar fashion to increase current by increasing the radii of theelectron orbits. Meanwhile, some accelerators adopt an electric-fieldacceleration method instead of induction one using a magnetic field. Inthat case, the above description holds true if the term“acceleration-magnetic-field strength” is interchanged with the term“electric-field acceleration” in FIG. 10. However, during an electroninjection period, a hybrid accelerator needs to control changes withtime both the acceleration-magnetic-field strength and thedeflection-magnetic-field strength so as to have predeterminedrelationships therebetween; it results in complexelectromagnet-power-supply controlling in which the electronacceleration unit and the electron deflection unit generate magneticfields, causing a problem in that the accelerator has been manufacturedat high costs. The above problem has also existed when an electric fieldacceleration method as well as induction one is used as an electronacceleration means. In that case, it results in complexity ofcontrolling power supply for the electric field acceleration andelectromagnet-power-supply that lets the electron deflection unitgenerate magnetic fields, causing a problem in that the accelerator hasbeen manufactured at high costs. Therefore, when it is intended toincrease current in the circular accelerator according to theabove-described method, it has been a common problem, not limited to thehybrid accelerator, that control of a power supply applying a highvoltage to an electron acceleration unit and a power supply supplyingcurrents to an electron deflection unit for generating a deflectingmagnetic field becomes complex, causing high costs.

SUMMARY OF THE INVENTION

The present invention provides a circular acceleration apparatuscomprising: a circular accelerator including an electron accelerationunit accelerating injected electrons, and a deflection-magnetic-fieldgenerating unit deflecting the orbits of the electrons accelerated bythe electron acceleration unit; an electron generator, to which a pulsedvoltage is applied, to generate electrons for injecting to the circularaccelerator in respond to the pulsed voltage; and a circuit elementwhich generates the pulsed voltage for providing to the electrongenerator by making the pulsed voltage applied to the electron generatorhave at least one of a slow rising edge and a slow falling edge.

Also the present invention provides a circular acceleration apparatuscomprising: a circular accelerator including an electron accelerationunit accelerating injected electrons, and a deflection-magnetic-fieldgenerating unit deflecting the orbits of the electrons accelerated bythe electron acceleration unit; and an electron generator, to which apulsed voltage is applied, to generate electrons for injecting into saidcircular accelerator based on the voltage of the rising or falling edgeof said pulsed voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an electromagnetic wave generatoraccording to Embodiment 1 of the present invention;

FIG. 2A is a diagram of waveforms of electromagnetic fields generated byan electron acceleration unit and an electron deflection unit in acircular accelerator according to Embodiment 1 of the present invention,and FIG. 2B is a diagram illustrating intervals of voltages applied toan electron generator in the circular accelerator according toEmbodiment 1 of the present invention;

FIG. 3 is a diagram illustrating the waveform of a pulsed high-voltagethat is applied to electron generator according to Embodiment 1 throughEmbodiment 3 of the present invention;

FIG. 4 is a diagram illustrating the waveform of a pulsed high-voltagethat is applied to the electron generator according to Embodiment 2 ofthe present invention;

FIG. 5 is an outlined circuit diagram of a high voltage power sourcethat applies a high voltage to an electron generator according toEmbodiment 4 of the present invention;

FIG. 6 is a diagram illustrating a relation of how energies of theelectrons generated by the electron generator spread with respect toacceleration current in the circular accelerator according to Embodiment1 of the present invention;

FIG. 7 is a sectional view of an electromagnetic wave generatoraccording to Embodiment 5 of the present invention;

FIG. 8 is an outlined configurational diagram of an X-ray imaging systemaccording to Embodiment 6 of the present invention;

FIG. 9 illustrated simulation results of images of a sphere having adiameter of one millimeter, taken by the X-ray imaging system accordingto Embodiment 6 of the present invention;

FIG. 10 is a diagram illustrating waveforms of strengths ofelectromagnetic fields generated by the electron acceleration unit andthe electron deflection unit in a circular acceleration apparatusrelated to background arts.

DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, embodiments according to the present invention areexplained based on figures.

Embodiment 1

An embodiment according to the present invention is that orbit radii ofelectrons in a circular accelerator are enlarged by injecting into thecircular accelerator electrons generated by an electron generator withtheir energies being varied. Applying this embodiment, even when thestrength of a deflection magnetic field changes with respect to time inthe same patterns as that of an acceleration magnetic field, it ispossible to enlarge orbit radii of electrons that have been injected andaccelerated, without controlling strength change with time of deflectionmagnetic field in a complicated manner as has been implemented in aconventional apparatus. Therefore, it becomes possible, in a simplifiedmanner, to reduce substantially spatial density of orbiting electrons,enabling large-current acceleration and storage. Hereinafter, first anoverall apparatus according to this embodiment will be outlined; then amethod of varying energies of electrons generated by the electrongenerator will be described.

FIG. 1 illustrates an electromagnetic wave generator, according toEmbodiment 1, equipped with a circular acceleration apparatus using ahybrid accelerator as the circular accelerator; FIG. 1 is also asectional view taken on an orbital plane in which electrons move inorbits. In FIG. 1, “1” is an electron generator for generatingelectrons, “2” is a circular accelerator-a hybrid accelerator isexemplified in the figure—for injecting thereinto the electronsgenerated by the electron generator 1 and for accelerating the electronsup to a predetermined energy while making them move in orbits. “3” is anelectromagnetic-wave-generation target that is placed in the way of anelectron orbit in the circular accelerator 2, and the electronsaccelerated up to the predetermined energy collide with the target 3 inorder to generate electromagnetic waves such as X-rays. “4” is a highvoltage power supply that applies the pulsed voltage to the electrongenerator 1 for generating electrons. All of the above-describedcomponents constitute the electromagnetic wave generator.

The components in the circular accelerator 2 (hereinafter, a hybridaccelerator is exemplified as the circular accelerator) will bedescribed in detail below. “11” is a vacuum chamber in which theelectrons orbit; “12” are orbits in which the electrons move in thevacuum chamber 11, and spread radially as shown in the figure. Here inthe figure, each of the orbits 12 is illustrated as a closed orbit;however as will be described later in detail, because the orbitingelectrons are being accelerated, they may move in the same fixed orbitsor in orbits continuously changing in a spiral fashion in response tostrength change with time of a deflection magnetic field. However, evenif the change occurs, the amount of radius change per turn is in generalimperceptible; approximately closed orbits 22 are configured. Therefore,hereinafter, the term “closed” will be used to imply the above meaningas well. In addition, the electron orbits illustrated in the figure arethe ones in which electrons can move stably; other stable orbits canexist between the ones illustrated in the figure. “13” is an electronacceleration unit for accelerating electrons moving in the orbits 12 inthe circular accelerator 2, “14” is an electron deflection unit fordeflecting, in a plane formed by the orbits 12, the electrons that aremoving and being accelerated. With a power supply, the electronacceleration unit 13 and the electron deflection unit 14 generatealternating magnetic fields having frequencies ranging from 50 hertz toseveral dozen kilohertz, they will be referred hereinafter to as anacceleration magnetic field and a deflection magnetic field,respectively.

As have been described, the electrons having been generated by theelectron acceleration unit 1 are injected into the circular accelerator2, undergo deflection force from the deflection magnetic field whilepassing through the electron deflection unit 14, and move in the closedorbits 12 in the vacuum chamber 11. While the electrons are moving inorbits, they are accelerated, when passing through the electronacceleration unit 13, by the electric field induced from theacceleration magnetic field generated by the electron acceleration unit13; the radii of the orbits can be changed in response to the strengthof the deflection magnetic field that is generated by the electrondeflection unit 14 and changes with respect to time. Electrons havingreached a predetermined energy level by being accelerated arecontrolled, using the above-described method, to move into an orbitwhere the target 3 is placed for generating electromagnetic waves suchas X-rays, so that the electrons collide with the target 3 so as togenerate electromagnetic waves such as X-rays in an electron-movingdirection.

Next, the manner of the injection into the circular accelerator 2 ofelectrons generated by the electron generator 1 will be described, usingFIG. 2. In FIG. 2, waveforms of acceleration-magnetic-field strength 21generated by the electron acceleration unit 13 in the circularaccelerator 2, deflection-magnetic-field strength 22 generated by theelectron deflection unit 14, and a pulsed high voltage 23 applied to theelectron generator 1 for generating electrons are illustrated withrespect to time. FIG. 3 is an enlarged view of the pulsed high voltage23. The energy of the electrons generated by the electron generator 1depends on the value of the pulsed high voltage 23 applied thereto.

It is assumed that the waveforms of the acceleration-magnetic-fieldstrength 21 and deflection-magnetic-field strength 22 are similar toeach other, such as approximately sinusoidal wave patterns that changewith time. In this case, adjusting to predetermined lengths the gapsbetween magnetic poles of the electron acceleration unit 13 and betweenthose of the electron deflection unit 14, it becomes possible that bothunits share a power supply. Thereby, it also becomes unnecessary tocontrol, in a complex manner, deflection-magnetic-field strength asillustrated in FIG. 10, so that a power supply can be manufactured atvery low costs. When magnetic fields are controlled, as described above,by waveforms similar to each other, the deflection-magnetic-fieldstrength increases in a manner similar to theacceleration-magnetic-field strength during injection periods; radialchange of the electron orbits during injection periods becomes less thanthe case shown in FIG. 10. Therefore, radii of the electron orbitsduring injection periods are expanded less than the case shown in FIG.10; the density of electrons becomes relatively high. To avoid thesituations above, fluctuations of electron energies at injection aredeliberately increased greatly in the electromagnetic wave generatoraccording to this embodiment; thereby, the radii of electron orbits areexpanded even in those situations, intending that the density ofelectrons is lowered. Using FIG. 2 and FIG. 3, details thereabout willbe described below.

In FIG. 2, after the strength of the magnetic field 21 generated by theelectron acceleration unit 13 and that of the magnetic field 22generated by the electron deflection unit 14 have risen to predeterminedvalues, the pulsed high voltage 23 illustrated in FIG. 3 is applied tothe electron generator 1. The pulsed high voltage is not the one thathas been generally applied to the electron generator 1, but has aslowly-rising edge. Each of the electrons generated by the electrongenerator 1 in FIG. 1 has its own energy corresponding to aninstantaneous value of the pulsed high voltage 23. The waveform of thepulsed high voltage has the dulled rising edge, which is generated inthe high voltage power supply. Shown in FIG. 3, the waveform of thepulsed high voltage 23 applied to the electron generator 1 is formed torise slowly up to its peak, for example, within some one microsecond.Meanwhile, in the circular accelerator, there exists a range ofinjection energy that allows the electrons to be accelerated stablyafter having been injected. As have been described above, electronsgenerated by the electron generator 1 obtain energies depending on apulsed high voltage value; the peak value of the pulse is determinedsuch that it copes with the upper limit value in the rage of injectionenergy. Meanwhile, the lower limit value in the rage of injection energycorresponds to a predetermined voltage value, as shown in FIG. 3, on thewaveform of the pulsed voltage rising slowly. Furthermore, there existsan upper limit of an injection period in the circular accelerator 2;this is because that injecting for too long period causes injectedelectrons to move unstably in orbits. Taking into account of theconditions above, while the pulsed high voltage 23 in FIG. 3 is beingapplied, an injection period is to be determined so that the electronsmove stably in orbits after having been injected. This injection periodis indicated as a first injection period 24 in FIG. 3. Therefore, whilethe pulsed high voltage 23 is being applied, electron energy generatedin response to the waveform during the first period 24 is low in theinitial part of the period, but increases high with passage of time;each of the electrons is injected into the circular accelerator 2 everytime it is generated. Electrons of low energies are injected in theinitial part of the period and accelerated therefrom so as to havelarger energies; therefore, their energies become close to those ofelectrons injected during the later part of the period within the firstinjection period 24. However, even under such circumstances, it ispossible to ensure that the electron orbits are sufficiently spread out.When the acceleration-magnetic-field strength 21 and thedeflection-magnetic-field strength 22 are correlated with each other insuch a manner that, when the electrons have a constant energy at eachinjected instant, if the electrons are made to move in a fixed orbitwithout regard to each injected instant, the electron orbits spread outradially due to energy differences among the injected electrons. In bothcases, without taking complex control of the acceleration-magnetic-fieldstrength 21 and deflection-magnetic-field strength 22, it is possiblethat the radii of the electron orbits are easily expanded by slowlyraising the leading edge of the pulsed high voltage 23 applied to theelectron generator 1; therefore, spatial charge of the electrons can bereduced, so that one of the initial aims to increase current can beachieved. Meanwhile, in the conventional application of pulsed voltageto the electron generator 1, injection of electrons begins when thepulsed voltage reaches a constant voltage, and ends at an instant duringthe period in which the pulsed voltage is yet maintained at the constantvoltage; that is, it is basically assumed that electrons having aconstant energy are injected. The electromagnetic wave generatoraccording to the embodiment differs completely from the related arts inthat injection begins at an instant before the pulsed voltage reaches aconstant voltage or continues until an instant after the voltage hasreached the constant voltage.

Using FIG. 6 as an example, an extent to which a current is increasedwill be explained as follows. FIG. 6 shows results of simulationcalculation of an acceleration current, taking as a parameter energyspread (energy difference) of electrons injected into the circularaccelerator 2, when the acceleration-magnetic-field strength 21 and thedeflection-magnetic-field strength 22 are controlled so that orbits arenot changed by acceleration. As seen from in the figure, as energies ofelectrons injected spread, the maximum value of the acceleration currentincreases. However, remarkable increase is not found in an energy spreadrange of below five percent, the reason for which is that stable orbitscorresponding to each of the energies differ a little from each other inthe energy spread range of below five percent; a beam size itselfcorresponding to each energy is considered as a dominant factor thatdetermines spatial charge effect. In an energy spread range of over fivepercent, acceleration-possible current increases dramatically; it almostlinearly increases until the energy spread reaches 15 percent thereof,as the energy spread increases; beyond that energy spread, theacceleration current increases gradually again. This is because, withenergy spread being widened too much, some of the electrons move beyonda stable orbit region of the circular accelerator 2, so that they do notmove stably in orbits. In FIG. 6, it is found that acceleration currentcan be increased up to five times as much or more. Furthermore,depending on a design of the accelerator, it is also possible toincrease the acceleration current up to ten times as much or more.

Next, in order to generate electromagnetic waves such as X-rays, it isnecessary for electrons moving in orbits to collide with theelectromagnetic-wave-generation target 3. In the example shown in FIG.1, the electron generator 1 is disposed in the outer side of thecircular accelerator 2, so that electrons are injected from thecircumference thereof, meanwhile, the electromagnetic-wave-generationtarget 3 is disposed in the inner side of the circular accelerator 2.Under the circumstances in which the acceleration-magnetic-fieldstrength 21 and the deflection-magnetic-field strength 22 change withrespect to time, as shown in FIG. 2, presetting the strength ratio ofthem at a predetermined value, the radii of the electron orbits can bereduced radially inward during their acceleration, depending on thevalue. As has been described above, the radii of the electron orbitsthat have been expanded radially in the circular accelerator 2 can begradually reduced inward by fixing the relation between theacceleration-magnetic-field strength 21 and thedeflection-magnetic-field strength 22 at a predetermined one; theelectrons can collide with the electromagnetic-wave-generation target 3so that electromagnetic waves such as X-rays are continuously generatedduring a period in which the radii of the orbits are reduced dependingon each distance (to the target). A similar effect can be obtained, whenthe radii of the orbits are changed by adding perturbation to thedeflection magnetic field at the time of acceleration completion, sothat electrons collide with the electromagnetic-wave-generation target3. As has been described, it is possible for the electron beams havingincreased current to collide with the electromagnetic-wave-generationtarget 3; even when the electromagnetic-wave-generation target 3 becomessmaller, electromagnetic waves such as X-rays of strength commensurateto the current can be generated. That is, it becomes possible to realizehigh brilliance electromagnetic waves.

So far, a hybrid accelerator has been exemplified as the circularaccelerator 2; however, a circular accelerator is not limited to thehybrid accelerator. As long as an accelerator can stably accelerateinjection electrons having energies in a certain range, the acceleratorcan bring effects similar to that described above; synchrotronaccelerators and betatron accelerators are examples of those.

However, the degree of improvement in increasing current differsdepending on types of accelerators, because each type has its own rangeof allowable injection energy. In addition, the above explanations havebeen made on the assumption that the electron acceleration unit 13 usesinducted magnetic field acceleration in which electrons are acceleratedby an electric field generated from an acceleration magnetic field.However, the above-described method is not limited to only the inducedmagnetic field acceleration, but also may be applied intact to highfrequency electric field acceleration. In that case, replacing theacceleration-magnetic-field strength 21 in FIG. 2 with anacceleration-electric-field strength, the above description holds true.

Embodiment 2

In the present embodiment, the pulsed high voltage 23 applied to theelectron accelerator 1 has a slow falling edge, and electrons generatedduring this slow falling period are injected into the circularaccelerator 2. The waveform of the pulsed high voltage has the dulledfalling edge, which is generated in the high voltage power supply. Whena second injection period 25 shown in FIG. 3 is used as an injectionperiod, it is also possible to use electrons with lower energies thathave been generated during the period of the falling edge of the pulsedhigh voltage 23. FIG. 4 is a diagram illustrating an example of awaveform of a pulsed high voltage 23 according to the embodiment.Because the falling edge of the pulse is used, any rising edge of thepulse is not critical. In the figure, a pulsed high voltage that risessteeply as in a conventional manner is shown. In the figure, ‘25’indicates a second injection period that is determined under constraintsof an injection energy range and an injection period needed for stableacceleration. That is, the second injection period starts at an instantduring a period in which the voltage holds its peak, and continues untila predetermined instant during a period of the voltage falling. In eachof FIG. 3 and FIG. 4, a high voltage applied to the electron generator 1is initially high, and then becomes lower with a lapse of time; inresponse to the voltage, electrons having high energies are initiallyinjected into the circular accelerator 2, and then those having lowenergy are injected thereinto with a lapse of time. Therefore, wheninjection is completed, the energies of injection electrons spreaddifferently from that in FIG. 3; the energy differences become largerthan those at their injection; accordingly, orbits of injected electronsspread out radially. As has been described above, the waveform of thepulsed high voltage 23 can be made to slowly fall at the falling edgeand a period corresponding to the edge is used to inject electrons, sothat the radii of electron orbits can also be expanded; therefore, it ispossible to increase current in the circular accelerator similarly toEmbodiment 1. Therefore, using a circular acceleration apparatus asdescribed above, it becomes possible to intensify electromagnetic wavessuch as X-rays generated by electromagnetic-wave generators such asX-ray ones.

Embodiment 3

In this embodiment, the injection period includes both of the firstinjection period 24 and the second injection period 25 in FIG. 3.Because the embodiment brings both effects described in Embodiment 1 andEmbodiment 2, the radii of the electron orbits can also be expanded, sothat it is possible to increase current in the circular acceleratorssimilarly to Embodiment 1. Therefore, using a circular accelerationapparatus as described above, it becomes possible to intensifyelectromagnetic waves such as X-rays generated by electromagnetic-wavegenerators such as X-ray ones. However, as has been described, theinjection period has an upper limit; in some cases, the periods eachdescribed in Embodiment 1 and Embodiment 2 can not be simply combined.In those cases, the overall pulse width may be narrowed so that thecombination of both periods is permissible as the injection period.

Embodiment 4

In this present embodiment, a means will be described below in which thepulsed high voltage 23 shown in FIG. 3 is applied to the electrongenerator 1. Conventional high voltage sources used for betatronaccelerators and such generate pulsed voltage by charging a capacitorwith electricity generated by a high voltage generator and switching thecharge with a vacuum tube such as a thyratron. However, the problem hasbeen that the high voltage sources become bulky and expensive, and thevacuum tube needs to be replaced frequently. In this embodimentaccording to the present invention, the pulsed high voltage shown inFIG. 3 can be generated by a simple power-supply circuit shown in FIG.5.

In order for an equivalent circuit 31 of the electron generator 1 togenerate predetermined high voltage pulses, low voltage pulses are firstgenerated. That is, an AC-voltage from an AC-power supply 32 isconverted into a DC-voltage with rectifying/smoothing circuits 33, andthe predetermined low voltage pulses are generated from the DC-voltageby a switching device 34 such as an insulated gate bipolar transistor(IGBT) or a metal oxide semiconductor field effect transistor (MOS-FET);then the pulses are stepped up into high voltage pulses through a highvoltage transformer 35. Because pulses are formed in the low voltageside thereof, it is easy to form the pulses into the ones of anywaveform, and the voltage transformer 35 can make the voltage riseslowly and can make the voltage increase monotonically at its risingedge; therefore, the pulsed high voltage 23 shown in FIG. 3 can easilybe formed. In addition, the circuit that generates the pulses can beconfigured with only low-price elements; therefore, manufacturing costsof the pulsed high voltage source can be dramatically reduced.

Embodiment 5

In Embodiment 1, the electromagnetic-wave-generation target 3 isdisplaced in an inner-side orbit of the electron orbits 12; the sameeffects as those in Embodiment 1 can be obtained when the target isdisposed, as shown in FIG. 7, in an outer-side orbit thereof. With anelectromagnet power supply, the electron acceleration unit 13 and theelectron deflection unit 14 generate AC magnetic fields havingfrequencies between 50 hertz and several dozen kilohertz; when therelation between magnetic field strengths of both the magnetic fields isset to a predetermined value, the electron beams do not change theirorbits largely, so that the electron beams are stably accelerated withina region. The electron beams having been accelerated are shifted outwardin response to slight change of the relation between magnetic fieldstrengths of the electron acceleration unit 13 and the electrondeflection unit 14; the electron beams collide with theelectromagnetic-wave-generation target 3 disposed in the way of an orbitin a stably orbiting region, so that electromagnetic waves such asX-rays are generated. Here, when the target 3 is disposed in the outerportion of the accelerator, part of the electron beams collide with thetarget 3 immediately after their injection. However, as long as thetarget 3 is on the order of several micrometers, the number of electronsthat collide with the target 3 when injected is small, and most of themcan be stably accelerated.

In that case, the electron beams are accelerated in a region inward fromthe location of the target 3 for generating electromagnetic waves suchas X-rays. After the acceleration has been finished, the radii of theelectron beam orbits are enlarged so that electrons are shifted to reachthe target 3 for generating electromagnetic waves such as X-rays.Detailed explanations of shifting the beams and generatingelectromagnetic waves such as X-rays are the same as those inEmbodiment 1. In addition, when electromagnetic waves such as X-rays aregenerated in a region close to the outer circumference of the circularaccelerator, the generating source that generates electromagnetic wavessuch as X-rays is disposed closer to an irradiation target than the casein which electromagnetic waves such as X-rays are generated in a regionnear to the center of the accelerator; therefore, it becomes possible toincrease irradiation density and shorten the period of irradiation.Furthermore, it becomes easy to increase imaging magnification. Increaseof imaging magnification can be realized by distancing the irradiationtarget apart from an imaging screen. Given that R1 is a distance betweenthe irradiation target and the generating source that generateselectromagnetic waves such as X-rays, R2, a distance between theirradiation target and the imaging screen, the imaging magnification isR2 divided by R1. Because R1 can be made smaller while keeping R1+R2constant, the imaging magnification becomes large. On the contrary, whenR1 is large in the first place, R2 must be increased in order to achievea high imaging magnification, which causes a problem in that not only alarge area is needed to install the imaging system, but also, becausethe imaging area becomes large, the strength of electromagnetic wavesper area that can be used for imaging becomes low, so that statisticalaccuracy in imaging data is decreased. In a case where R1 is kept small,an irradiation area becomes small by that much.

Embodiment 6

FIG. 8 is an outlined configurational diagram of an X-ray imaging system(an electromagnetic-wave imaging system, in broad sense) according tothis embodiment. The imaging system includes an electromagnetic wavegenerator 71, a subject-a human body 72 here, an image detector 73, anda data processing unit 74. Intensified X-rays 75 that have beengenerated by the electromagnetic wave generator 71 are incident on thehuman body 72, are detected by the image detector 73, and then areprocessed by the data processing unit 74 so as to produce a radioscopicimage. Because the electromagnetic wave generator 71 can generateintensified X-rays whose radiation-source size ranges from severalmicrometers to approximately dozen micrometers, refraction-contrastimaging can be implemented in which minute refractions in X-rays areused. Because of small refraction effects, this method has not beenimplemented until the size of radiation source becomes sufficientlysmall. However, provided that the size of radiation source is small, theX-ray strength is generally decreased; it has been difficult to produceimages with sufficient statistical accuracy. Therefore, conventionally,the method has only been realized in a highintensified-synchrotron-radiation generator—such as Super Photon ring 8GeV (SPring8)—having a diameter of several hundreds meters, so thatprogress has not been made in medical use; however, refraction-contrastimages can be obtained by using an electromagnetic wave generator 71,according to the present invention, whose size is almost equal to orsmaller than that of a conventional X-ray tube; therefore, medical useof the method is expected to be promoted. Using the method ofrefraction-contrast imaging, mixture of minute materials havingdifferent mass-densities can be imaged with their boundaries beingreinforced, and enlarged images of them can also be obtained; therefore,it is possible to perceive a small cancer of approximately severalmillimeters. In addition, because the images taken by therefraction-contrast imaging method can realize contrast ten times ashigh as those by the conventional absorption-contrast imaging method,the images can be taken with a subject being exposed to a radiation doseof approximately one tenth of that compared to conventional imagingmethods.

FIG. 9 shows a result, in which the system shown in FIG. 8 has simulateda radioscopic image of a sphere of one millimeter diameter, made ofwater-equivalent material, which is assumed as a small cancer. It isassumed that the size of target is ten micrometers; an accelerationenergy of the electron beams is one mega-electron volt; a beam currentvalue is, when ΔE/E of the injection beam is 15 percent, two amperes.‘81’ is a conventional absorption-contrast image, ‘82’, arefraction-contrast image. A circular line that appears well-defined inthe refraction-contrast image 82 is a boundary of the water-equivalentsphere, and difference from the one in the absorption-contrast image 81is pronounced. The refraction-contrast imaging method above-describedcan be used only because its radiation source is small and has highstrength. Herewith, a meaning has been verified in which a radiationsource according to the present invention is used as the one for X-rayimaging systems. This holds true not only for X-rays, obviously, butalso for all other electromagnetic waves.

Furthermore, human bodies are not only the imaging subjects of the X-rayimaging systems; for example, when producing a radioscopic image of apower semiconductor device by the systems provided with therefraction-contrast imaging method, aluminum wirings in the device canbe perceived by the refraction-contrast imaging method, in which thewirings have not been perceived by the conventional absorption-contrastimaging method. Because the refraction-contrast imaging method candistinguish two kinds of materials whose atomic numbers are close toeach other, the method can also distinguish aluminum wirings whoseatomic number is close to that of silicon.

Although, in the above explanation, the circuit element, which dulls atleast one edge of the rising and the falling edge of the pulsed highvoltage, has been provided in the high voltage power supply, the circuitelement may be provided outside of the high voltage power supply.

According to these embodiments, because a simplified high voltage powersupply is adopted, it is possible to obtain a circular accelerationapparatus that can accelerate higher currents as well as avoid complexcontrolling of a deflecting magnetic field generated by an electrondeflection unit. Also, applying the circular acceleration apparatus toan electromagnetic wave generator and an electromagnetic-wave imagingsystem using the electromagnetic wave generator, a generator that cangenerate intensified electromagnetic waves such as X-rays and anelectromagnetic-wave imaging system that has a high resolution can beobtained.

Although, as described above, the embodiments according to the presentinvention have been explained with referring to the figures, specificstructures are not limited to these embodiments, but other structuresmay be included in the invention without departing from the spirit andscope thereof.

1. A circular acceleration apparatus comprising: a circular acceleratorincluding an electron acceleration unit accelerating injected electrons,and a deflection-magnetic-field generating unit deflecting the orbits ofthe electrons accelerated by said electron acceleration unit; anelectron generator, to which a pulsed voltage is applied, to generateelectrons for injecting to said circular accelerator in respond to thepulsed voltage; and a circuit element which generates the pulsed voltagefor providing to said electron generator by making the pulsed voltageapplied to the electron generator have at least one of a slow risingedge and a slow falling edge.
 2. A circular acceleration apparatusaccording to claim 1, wherein said circuit element generates the pulsedvoltage for providing to said electron generator by dulling at least oneof rising and falling edge of the waveform of the pulsed voltagegenerated by a high voltage power supply.
 3. A circular accelerationapparatus according to claim 1, comprising a high voltage power supply,and wherein said high voltage power supply includes said circuitelement.
 4. A circular acceleration apparatus according to claim 1,wherein electrons generated based on the voltage of the rising orfalling edge of the said pulsed voltage, are injected into said circularaccelerator.
 5. A circular acceleration apparatus according to claim 1,wherein electrons generated for the rising period where the value ofvoltage increases, are injected into said circular accelerator.
 6. Acircular acceleration apparatus according to claim 1, wherein electronsgenerated for the falling period where the value of voltage decreases,are injected into said circular accelerator.
 7. A circular accelerationapparatus according to claim 5, wherein electrons generated for thepeak-value period where the peak value of the voltage maintains, arealso injected into said circular accelerator.
 8. A circular accelerationapparatus according to claim 6, wherein electrons generated for thepeak-value period where the peak value of the voltage maintains, arealso injected into said circular accelerator.
 9. A circular accelerationapparatus according to claim 1, wherein said electron acceleration unitaccelerates electrons through induction acceleration.
 10. A circularacceleration apparatus according to claim 3, wherein said high voltagepower supply has a low voltage pulse generating circuit generating a lowvoltage pulse, and said circuit element has a transformer connected tosaid low voltage generating circuit, to generate said pulsed voltage forproviding to said electron generator by the pressure rising of the lowvoltage pulse.
 11. A circular acceleration apparatus according to claim10, wherein said low voltage pulse generating circuit includes an ACvoltage source, rectifying/smoothing circuit connected to AC voltagesource to convert the AC voltage supplied from said AC voltage source tothe DC voltage, and a switching device connected to saidrectifying/smoothing circuit to generate said low voltage pulse byswitching.
 12. A circular acceleration apparatus according to claim 1,wherein the waveform of the strength of magnetic field generated by saidelectron acceleration unit is similar to that of magnetic fieldgenerated by said deflection-magnetic-field generating unit.
 13. Acircular acceleration apparatus according to claim 12, wherein saidwaveform of the strength of magnetic field generated by said electronacceleration unit has the same phase and period as that of magneticfield generated by said deflection-magnetic-field generating unit.
 14. Acircular acceleration apparatus comprising: a circular acceleratorincluding an electron acceleration unit accelerating injected electrons,and a deflection-magnetic-field generating unit deflecting the orbits ofthe electrons accelerated by said electron acceleration unit; and anelectron generator, to which a pulsed voltage is applied, to generateelectrons for injecting into said circular accelerator based on thevoltage of the rising or falling edge of said pulsed voltage.
 15. Anelectromagnetic wave generation apparatus comprising: a circularacceleration apparatus including a circular accelerator including anelectron acceleration unit accelerating injected electrons and adeflection-magnetic-field generating unit deflecting the orbits of theelectrons accelerated by said electron acceleration unit, an electrongenerator to which a pulsed voltage is applied to generate electrons forinjecting to said circular accelerator in respond to the pulsed voltage,and a circuit element which generates the pulsed voltage for providingto said electron generator by making the pulsed voltage applied to theelectron generator have at least one of a slow rising edge and a slowfalling edge; and an electromagnetic-wave-generation target, placed inthe way of an orbit in which electrons move stably in said circularaccelerator for generating electromagnetic waves by collision with theelectrons.
 16. An electromagnetic wave imaging system comprising: acircular acceleration apparatus including a circular acceleratorincluding an electron acceleration unit accelerating injected electronsand a deflection-magnetic-field generating unit deflecting the orbits ofthe electrons accelerated by said electron acceleration unit, anelectron generator to which a pulsed voltage is applied to generateelectrons for injecting to said circular accelerator in respond to thepulsed voltage, and a circuit element which generates the pulsed voltagefor providing to said electron generator by making the pulsed voltageapplied to the electron generator have at least one of a slow risingedge and a slow falling edge; an electromagnetic-wave-generation target,placed in the way of an orbit in which electrons move stably in saidcircular accelerator for generating electromagnetic waves by collisionwith the electrons; a measuring unit measuring said electromagneticwaves generated by the collision; and a data processing unit processingdata measured by the measuring unit.